The strive for higher simple cycle efficiency among gas turbine manufacturers has led to higher pressure ratios exceeding the supply pressures of gaseous fuels, e.g. natural gas. To overcome this insufficiency booster compressors for the gaseous fuel are used. Such separate compressors are driven by an electrical motor or by a high pressure fluid bled from the compressor or the turbine stage, as disclosed, e.g., in US 2004/0088987 A1 or U.S. Pat. No. 5,329,757. Similar systems are also known from gaseous fuel engines, as disclosed, e.g. in U.S. Pat. No. 5,899,070. If the compressor is used which is driven by air bled from the compressor or combustion gas bled from the turbine section, the air or gas, respectively, is expanded through a turbine connected to the fuel compressor.
U.S. Pat. No. 5,329,757 further discloses a heat exchanger which is used to cool the compressed gaseous fuel after compression. Furthermore, a second heat exchanger may be present in the duct ducting pressurised gas for driving the turbine connected to the fuel compressor. This heat exchanger is used for heating pressurised driving gas if this is relatively cool, e.g. gas from the compressor section, in order to increase its energy per unit mass. The heat is taken from the exhaust gas of the gas turbine engine.
A heat exchanger for heating fuel before injection into a combustor is disclosed in U.S. Pat. No. 6,817,187 B2.